1. Field of the Invention
The present invention relates to an impedance-matching device for an RF transmitter power amplifier circuit, and more particularly to an impedance-matching device in the form of a printed circuit which does not require any adjustment over the 88-108 MHz FM broadcast band.
2. Prior Art
It is common to provide an impedance-matching device between the input of an RF transmitter power amplifier stage and the output of an RF intermediate power amplifier stage. These matching devices are generally in the form of L, T or .pi. networks, and sometimes incorporate inductive coupling. The choice of which circuit to use is made on the basis of other components, and circuit parameters which are independent of impedance-matching considerations. All of such prior art circuits require adjustment of one or more circuit elements to satisfactorily provide an impedance-match over a specified range of frequencies and RF power levels. For example, a typical prior art impedance-matching device may incorporate a series coil having a variable inductance which is adjustable by moving a slug within the coil, using mechanical linkages such as gears and the like, for control from the front panel of the transmitter. This type of arrangement is relatively complicated and requires adjustments. In general, such circuits are not characterized by high reliability, because the mechanical linkages are not particularly stable, and the elements of such linkages are sometimes sensitive to vibration and may be michrophonic.